This invention relates to gaseous fuel heating by a regenerative fuel heating system in a combined cycle cogeneration power plant.
Conventionally, a preferred combined cycle cogeneration power plant configuration includes at least one combustion turbine (which is also referred to as "gas turbine") driving an electrical generator for receiving combustion fuel, a combustion turbine having a multi-stage compressor for compressing ambient air, a combustion turbine having a combustor for the combustion process, and a combustion turbine having turbine blades for expanding the gaseous combustion product through the turbine blades. A heat recovery steam generator (HRSG) receives the gaseous combustion product from the combustion turbine for generating motive steam and includes a superheater, reheater, evaporator, economizer, preheater and steam/water evaporator drums. A steam turbine which drives an electrical generator for accepting motive steam from the HRSG, includes an extraction port for extracting steam for the process, an induction port for accepting induction steam, a reheat port for accepting reheat steam from the HRSG and a condensing port to release exhausted steam into condenser.
It is generally recognized that the most significant technique for improving efficiency of power plant generation is by means of a combined cycle cogeneration power plant system. Increasing power plant efficiency and power output have been a continuous goal throughout the power industry. One such goal has been in the area of fuel heating in the combined cycle cogeneration power plant.
Several known prior art systems have sought to improve plant efficiency and power output by means of preheating fuel by utilizing economizer water from the HRSG, preheating fuel by utilizing exhaust gas from the combustion turbine, preheating fuel by a second heat recovery system in the combustion turbine exhaust gas flow path or preheating fuel by recovering hot air or steam from a combustion turbine engine.
One approach described in U.S. Pat. No. 4,932,204 recovers heat available in the exhaust gas by increasing the water flow through the economizer section of the HRSG to a rate in excess of that required to match the steam production rate in the evaporator section. The excess water flow is withdrawn from the HRSG at a temperature approaching the evaporator temperature and used to preheat fuel delivered to the combustion turbine.
Another approach is taught by U.S. Pat. No. 5,357,746, which preheats fuel by utilizing exhaust gas from the combustion turbine by a second heat recovery system, using waste heat from the combustion turbine that is not recoverable from the first heat recovery system.
Yet another approach is taught by U.S. Pat. No. 5,826,430, which preheats fuel by using heated coolant such as steam or air returning from the gas turbine engine.
Still another approach is taught by U.S. Pat. No. 5,845,481, which preheats fuel by a fuel line disposed in heat transfer relationship within the exhaust gas from the combustion turbine so that the fuel may be heated by the exhaust gas prior to being introduced into the combustor.
Such prior art systems have failed to recognize that the most efficient power plant has already been achieved through a combined cycle cogeneration power plant configuration. In addition, such prior art systems have all failed to recognize that there would be no additional energy recoverable without imposing penalties on the most efficient combined cycle cogeneration power plant.